This invention relates to the automatic protection of machines having an input and output of stock from damage due to jamming of the stock. This system is designed to detect a jammed part in a machine, and in particular, a punch press before additional parts are formed, or malformed as the case may be, and before the machine is damaged.
In any process where there is a continuous or intermittent feed of stock, damage to highly expensive machinery and waste of stock is probable if the machine jams. Accordingly, it is highly advantageous to have a safety system which detects a malfunction and turns off the machine as quickly as possible. If the machine is a punch press, it is particularly important to have a protection system. The high forces and rapid motion of a press can cause considerable damage in a brief period of time if the machine malfunctions.
It is desirable for a protection system to work automatically for all modes of operation of the machine. That is, any manual operation of the protection system during start-up or stopping of the machine increases the chances of a mistake. This desirable and important advantage of automatic operation is not normally present since an output sensor does not observe anything during start-up until some stock has actually passed through the machine. Similarly, the output sees material for a short duration after the input has ceased. Thus, there are periods when the input and output are not seeing material simultaneously. Comparisons of the input and output must compensate for these transient situations if the system is to be automatic.
Machine protection has been the subject of previous devices but all such systems have deficiencies. Jensen U.S. Pat. No. 3,348,440 discloses a sequence control for an automatic machine but is highly elaborate and expensive. U.S. Pat. No. 3,122,796 recognizes a similar problem in a printing machine where accumulations of stock may cause damage. However, the patent utilizes a light-responsive electrical device which is not always the most desirable. Moreover, neither of the above-noted machines correlate the output material with the input material to determine if the machine is functioning correctly. Weiland U.S. Pat. No. 3,543,621 discloses the recognition that punch presses or similar machines may malfunction if jamming occurs. However, it also does not correlate the input and output of the press with a timing mechanism to coordinate the protection of the machine during operation. Moreover, the prior art does not appear to function automatically for all modes of machine operation.
This invention utilizes an apparatus and process which more fully monitors the functions of a punch press and reacts quickly to any malfunction. The utilization of sensors at the input and output, a timing signal, memory and comparators permit stoppage of the machine as quickly as possible in order to minimize damage to stock and to the machine itself. The memory, which correlates the input/output sensor impulses with a timing signal, is particularly advantageous since it makes a comparison of the various functions of the machine for all modes of transient and continuous operation.